DESCRIPTION (Applicant's Description-edited) This proposal aims to refine the Kaiser Permanente Northwest Region's Benign Breast Disease (BBD) Registry and to make its availability known to qualified researchers who want to learn more about the relationship between BBD and breast cancer and the genetic changes that lead to breast malignancy. The Benign Breast Disease Registry includes data on 9,683 women with benign breast disease diagnosed between 1970 and 1994. Available through the registry are histologic classification at the time of diagnosis and subsequent breast cancer status, as well as archived tissue for benign and malignant tumors. Because using historically-diagnosed benign breast disease is problematic, we propose to refine this resource by reviewing the histopathologic classification of benign breast disease using current criteria. This will provide a resource of consistently classified subgroups of benign breast disease with long follow-up for breast cancer occurrences. Specifically, we will update the breast cancer status of women in the Benign Breast Disease Registry from the KPNW Tumor Registry, document the availability and quality of benign breast tissue samples, and review all of the archived material available in KPNW prior to the development of breast cancer. We will include all women with subsequent breast cancer (estimated N=218); among women without breast cancer, we will include all those with proliferative changes in the original diagnosis (estimate N=983), and a sample of those with an original diagnosis of nonproliferative disease (N=500). We will assess agreement between original and current diagnoses and the percent of cases "upgraded" to a higher-risk type of benign breast disease. Finally, we will make known the availability of this public domain Benign Breast Disease Registry for collaborative efforts. Because of the availability of both benign and malignant archived tissue collected over time from the same women, the pilot phase of the KPNW Benign Breast Disease Registry will provide an important resource to investigators interested in the relationship between benign breast disease and breast cancer, including the associated genetic changes.